Growing garnet on non-garnet single crystal



Feh.25, 1969 J. E. MEE' 3,429,740

GROWING GARNET ON NON-GARNET SINGLE CRYSTAE Filed Sept. 24. 1965 INVENTOR.

JACK E. MEE

ATTORNQEY United States Patent 3,429,740 GROWING GARNET 0N NON-GARNET SINGLE CRYSTAL Jack E. Mee, Anaheim, Calif., assignor to North American Rockwell Corporation Filed Sept. 24, 1965, Ser. No. 489,930 US. Cl. 117-106 Int. Cl. B011 17/30 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to garnet crystals grown on nongarnet substrates and to a chemical vapor deposition process for growing garnet crystals epitaxially on non-garnet substrates.

Crystals with the garnet structure have become important technologically and scientifically in recent years. Many of the crystals have magnetic properties which make them useful for device purposes. For example, thin crystals of certain of the magnetic garnets are transparent and display a magneto-optic eifect when polarized light impinges on the crystal. Such magneto-optic etfect can be used for display purposes. Scientifically, this effect can be used to study magnetic domain structures, electronic absorption spectra, etc. Even non-magnetic garnets have useful device properties, e.g., Y Al O may be used as a laser host material.

Single crystal garnets are grown by Verneuil, hydrothermal and flux techniques. Commercially they are usually grown by the flux techniques wherein the garnet is grown from a molten salt solution. These methods are not adaptable to growing high quality, thin single crystal garnet films.

It is important to have the films as free of defects as possible in order to make the greatest use of them. This is best accomplished ,by chemical vapor deposition since the garnet films can be used as grown whereas garnets grown by other techniques must be cut and mechanically polished thereby introducing many defects.

The characterizing feature of this invention is a cornposite of single crystal garnet on a single crystal substrate which is not within the garnet class. The epitaxial single crystal garnet film may be grown by a chemical vapor deposition process on large areas.

Garnet is defined herein as a solid material having the formula {M [M (M 0 where M is defined herein as at least one element selected from the class consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Ym, Yb, Lu, Ca and Bi; M is defined herein as at least one element selected from the class consisting of Fe, In, Sc, Mg, Zr, Sb, Al and Ga; and M is defined herein as at least one element selected from the class consisting of Fe, Al, Ga, Si, Ge and V. Particularly preferred because of their magnetic properties are the rare earth iron garnets. Particularly preferred of this class of garnet materials are Y Fe O and Gd Fe O while the preferred non-magnetic garnet is Y Al O In the above formula, the notations represent sites in the garnet material designated 0, a, and d sites respectively. Elements known to exist in these sites in the garnets are listed below and designated as to their oxidation state:

Garnets may be defined as pure, mixed or substituted. Typical examples of pure garnets are Y Fe O and Tb Fe O Examples of mixed garnets include where x may have a maximum value of 0.5, 1.3, 2, 1.4, 0.35 respectively for the preceding examples. Although La, Pr and Nd exist in mixed garnets, they do not exist in pure garnets such as La Fe O Pr Fe O and Nd Fe O A garnet with any other type of substitution is called a substitution garnet, for example, {Y [F62] (Fe Al 0 and 3x x [FEZ] 3-x x) l2- Other Fe containing garnets include Sm Fe O It is an object of this invention to provide single crystal garnet crystallographically bonded to a single crystal nongarnet structure.

Another object of this invention is to provide a composition having a large area of single crystal garnet on a non-garnet substrate.

Still another object of this invention is to provide a process for producing single crystal garnet on single crystal non-garnet substrates in large quantities.

These and other objects of this invention will become more apparent when considered in connection with the following description and drawings in which:

FIGURE 1 is a representation of an apparatus used in growing single crystal garnet on a single crystal nongarnet substrate.

Referring now to FIGURE 1, the apparatus of the present invention comprises a chamber 1, including inlet means 2 for injecting gases into one end of the chamber 1, and an exhaust 5 at the other end of the chamber. The chamber is surrounded by heater elements 6, 7 and 8 for controlling the temperature at locations within the chamber. Supported inside chamber 1 are a plurality of spaced crucibles 10 and 11. The crucibles are spaced to be within the area heated by respective heater elements. Also within the chamber is a quartz holder 13 on which substrates or seed crystals 12 are supported. The terms substrate and crystals are used interchangeably herein. The crystals are located in chamber 1 so that they are exposed to a mixture of gases flowing from inlets 2 and 14. Inlet 2 is connected to a source (not shown) of inert carrier gases such as helium and argon. Inlet 14 is connected to a source (not shown) of gases such as oxygen and water vapor, carbon dioxide and hydrogen.

The substrates 12 on which the garnet crystal material is deposited or grown are comprised of single crystal nongarnet type materials. For purposes of describing the composition produced by the process, the substrate material selected is MgO, although other substrate materials, for example, MgAl O lit-A and other materials having the formula Me'Mei'O, may also be utilized in producing the structure. The term Me may be Li, Mg, Mn, Fe, Co, Ni, Cu, Zn, or Cd and Me" may be Al, Cr, Mn, Fe, Ti.

It should be pointed out that the process is not limited to the particular chamber illustrated in FIGURE 1... Other chambers such as that described in an application entitled Ferrite Memory Device, Ser. No. 428,158, filed Ian. 26, 1965 may also be used as well as the chambers described in an application entitled Epitaxial Dielectric MgO Crystals, Ser. No. 424,417, filed Jan. 8, 1965, now US. Patent No. 3,386,852. The chamber components may be comprised of quartz, alumina or other suitable materials not causing contamination of the resulting garnet structure.

The substrates 12 may be prepared by cleaving optical grade MgO along a {100} cleavage plane or by cutting the MgO in the plane of desired configuration along its other crystal faces. The substrates are ground flat to produce a crystal having a selected size and a selected crystallographic plane and chemically polished in an acid etch solution. The substrates 12 are supported on the holder 13 inside chamber 1 and a garnet layer may be deposited as described in detail hereinafter.

The source materials 15 and 16 for producing the garnet deposit on the substrates 12 are placed in containers and 11 and heated to vaporization by heater elements 6 and 7 respectively. Metal halides used as source materials are placed inside containers 10 and 11. The halides include those of the metallic elements Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca and Bi in one container, and Fe, In, Sc, Mg, Zr, Sb, Al, Ga, Si, Ge and V in the other. When heated, the solid metal halides slowly vaporize.

Simultaneously with the heating of the above materials and 16, the above described gases are emitted through inlets 2 and 14. The plurality of gases including a source of available oxygen and the source material vapors react at the heated surface of the substrate to epitaxially deposit single crystal garnet on the non-garnet substrates.

After the garnet layer has been deposited on the substrate, the composition may be removed and placed in other environments, for example, a conventional vacuum deposition chamber (not shown) for further processing, depending upon the particular use intended for the composition.

To form the preferred rate-earth iron garnet structures, the corresponding halides of iron and of the desired rare earth metals are selected. Thus to form the particularly preferred structures the halides of yttrium, gadolinium and iron will be utilized. The choice of particular halide, such as chloride, bromide, iodide or fluoride will be determined by its decomposition temperature and other factors known to those skilled in the art.

The practice of the inventive methods for producing a single crystal garnet crystal on a non-garnet crystal substrate is described more fully with reference to the following examples:

Example I A substrate material, MgO, is prepared by cleaving the crystal along a {100} cleavage plane into approximately 18 mm. x 12 mm. dimensions. After cleaving, the substrate is mechanically ground flat on a series of metallographic papers to the 4/0 size. They are then chemically polished in a concentrated H PO etching solution heated to 125 C. for minutes. After the etching the substrates are given a thorough hot water rinse.

A quartz or alumina cylindrical shaped apparatus of FIGURE 1 having a 54 mm. ID. is utilized as the deposition chamber. A quartz or alumina holder is used to support the MgO crystal in the middle of the chamber. Quartz or alumina crucibles 10 and 11 contain source materials 15 and 16. The crucibles are each carefully located in the chamber with each source material having individually controlled electrical heater elements 6 and 7. In this example, the source materials are the metal halides FeBr and YC1 The temperature for the FeBr is held at 700 C. and the YCl is held at 1150 C. to give sufficient vapor pressures for the two reactants. The crystal is maintained at 1150 C. After the crystals and the containers are properly located in the chamber and heated to the appropriate temperature, argon at 1 ft. /hr. is passed through inlet 2 and carries the FeBr and YCl vapors to the MgO crystal. Oxygen at 1 ftfi/hr. is bubbled through water at room temperature and brought into the reaction area just in front of the MgO crystal through the opening provided by a 10 mm. ID. Vycor or alumina tube at one end of the chamber, shown in FIGURE 1 as opening 14. The H 0, 0 FeBr and YCl vapors react in the area of the MgO crystal. The reaction is continued for one hour, then the furnaces and the substrate are permitted to cool for approximately two hours. The garnet film formed is approximately five microns thick over an area of 18 mm. x 12 mm. The film displays the characteristics ferromagnetic properties of yttrium iron garnet and is identified by X-ray diffraction techniques.

The reaction to form the garnet layer can be represented as follows:

fi atz) 'az) 1920(1) g wn where (g) is gas and (s) is solid.

Example II The process and apparatus as described in connection with Example I is utilized in this example except that AlCl at C. and YCl at 1150 C. are used in place of the source materials described therein. Instead of oxygen, argon is bubbled through water to produce an H O vapor. The reaction to form the garnet layer can be represented as follows:

1150 G. 3YCI 511101; 121120 1) Y3Al5012(s) 214F101 MgO seed Example III The process and apparatus as described in connection with Example I is utilized in this example except that in lieu of the MgO crystal prepared as described, a flat tit-A1 0 (sapphire) crystal which has been mechanically and chemically polished is used as the substrate. GdCl is used in place of YCl The reaction to form the garnet layer can be represented as follows:

sapphire seed 2Gd3FB5012 181161) QOHBIX fiGdC am) 10FeBr 19112009 gong) Example IV The process and apparatus as described in connection with Example I is utilized in this example, except that GdI at -1000 C. is used in place of the YCl The reaction to form the garnet layer can be represented as follows:

6Gd 3(g) loFeBrm) 19112 g ne) Example V distilled water rinse.

Example VI The process and apparatus as described in Example V except that a {111} MgO plane is used rather than a {110} plane.

Example VII (110) or (111) MgO seed fi 'am I FB zm 19mm.) goat.)

I claim:

1. A composite comprising a monocrystalline substrate of non-garnet material and an epitaxial film of single crystal garnet material on said substrate, said substrate being selected from the class consisting of MgO, rat-A1 and MeMe" O wherein Me is selected from the class consisting of Li, Mg, Mn, Fe, Co, Ni, Cu, Zn and Cd and wherein Me is selected from the class consisting of A1, Cr, Mn, Fe and Ti.

2. A composite according to claim 1 wherein said single crystal garnet material is selected from the class consisting Of Y3F5O12, Gd3F5O12 and Y3Al50 2.

3. A composite according to claim 1 wherein said single crystal garnet material is Y Fe O and wherein said substrate is single crystal MgO.

4. A process for epitaxially growing garnet single crystals on a non-gamet single crystal substrate selected from the class consisting of MgO, a-Al O and MeMe" O wherein Me is selected from the class consisting of Li, Mg, Mn, Fe, Co, Ni, Cu, Zn, and Cd and wherein Me" is selected from the class consisting of Al, Cr, Mn, Fe and Ti, said process comprising the steps of:

heating said substrate,

vaporizing halides of the constituent metals of said garnet, and

transporting said vaporizing halides and an oxygenproviding gas to adjacent said heated substrate, whereby said halides and said gas react at said heated non-garnet substrate to deposit epitaxially a single crystal garnet film on said substrate.

5. The process as recited in claim 4 wherein said gases include decomposible halides of iron and of the rareearth metals.

6. The process as recited in claim 4 wherein said substrate comprises MgO having a deposition surface, and wherein said halides include an iron halide and at least one rare-earth metal halide selected from the class consisting of gadolinium and yttrium halides.

7. The process as recited in claim 4 wherein said deposited garnet crystal film is selected from the class consisting Of Y3F5012, Gd Fe O and Y3A15012.

8. The process as recited in claim 4 wherein said halides include a yttrium halide and an aluminum halide.

9. The process as recited in claim 4 wherein said vaporized halides are transported in an inert carrier gas.

References Cited UNITED STATES PATENTS 4/1964 Gambino 117-106 X 

